From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH 01/15] atomic: introduce atomic operations
Date: Wed, 08 Aug 2012 15:49:42 +0200
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Cc: kvm@vger.kernel.org, Stefan Hajnoczi <stefanha@gmail.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
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	Anthony Liguori <anthony@codemonkey.ws>,
	Jan Kiszka <jan.kiszka@siemens.com>,
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To: Peter Maydell <peter.maydell@linaro.org>
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Il 08/08/2012 15:32, Peter Maydell ha scritto:
>> > 1. GCC atomics look ugly, :) do not provide rmb/wmb, and in some
>> > versions of GCC mb is known to be (wrongly) a no-op.
>> >
>> > 2. glib atomics do not provide mb/rmb/wmb either, and
>> > g_atomic_int_get/g_atomic_int_set are inefficient: they add barriers
>> > everywhere, while it is clearer if you put barriers manually, and you
>> > often do not need barriers in the get side.  glib atomics also do not
>> > provide xchg.
> These are arguments in favour of "don't try to use atomic ops" --
> if serious large projects like GCC and glib can't produce working
> efficient implementations for all target architectures, what chance
> do we have?

Well, maybe... but the flaws in both GCC and glib are small in size
(even though large in importance, at least for us) and we can work
around them easily.  mb/rmb/wmb is essentially the small set of atomic
operations that we're already using.

Paolo